1. Technical Field
This invention relates to the field of internal combustion (IC) engine diagnostics and control. More particularly, it relates to an IC engine diagnostic system that uses the peak and integration values of an ionization current signal to perform engine diagnostics.
2. Discussion
Combustion of an air/fuel mixture in the combustion chamber of an internal combustion (IC) engine produces ions that can be detected. If a voltage is applied across a spark plug gap, these ions are attracted and will create a current. This current produces a signal called an ionization current signal IION that may be detected. After the ionization current signal IION is detected, the signal may be processed within a powertrain control module (PCM) for engine diagnostics and closed-loop engine combustion control. Various methods may be used to detect and process the ionization current signals that are produced in a combustion chamber of an internal combustion engine.
FIG. 3 illustrates an ionization current signal processing circuit that samples ionization current signals directly, e.g., using an analog-to-digital (A/D) converter 110, and then processes the sampled ionization current signal IION in a microprocessor 120. This circuit samples the ionization current signals at every crank degree of resolution over the compression and expansion strokes. This circuit also processes signals and performs engine diagnostic routines in a separate microprocessor 120 rather than in the powertrain control module (PCM) main processor 130, which lacks sufficient operating speed and memory 140 to handle the data sampling rate from the A/D converter 110. The use of a separate microprocessor 120 to process the increased data sample rate raises the manufacturing cost. In addition, the separate microprocessor 120 must have sufficient operating speed and memory to process the data samples from the A/D converter 110, thereby further increasing manufacturing cost.